The present invention relates to threaded rod assemblies, and in particular to threaded rod assemblies having flexible threaded rods.
Many mechanical assembly applications require connections or adjustments in relatively inaccessible locations. Until now, such connections and adjustments have required either partial or complete disassembly of the equipment, or relatively complex designs including access panels or access holes. These designs increase the cost of the equipment and generally result in difficult or at least inconvenient assembly or adjustment procedures. These problems arise from the inherent nature of threaded fasteners or rods that advance and retract only in straight lines along a longitudinal axis. Many such assemblies and adjustments would be greatly simplified if these threaded fasteners could turn corners. However, conventional metal threaded fasteners and bolts are so inherently rigid as to prohibit the twisting and turning required to change directions.
The present invention provides a threaded element with sufficient flexibility to make substantial bends, while retaining sufficient strength and rigidity to function in applications requiring rigid connections and fine, accurate and repeatable adjustments.
According to principles of the present invention, a flexible metallic bolt assembly is provided. The assembly includes a flexible threaded rod formed of a helical coil tension spring and having a rotary drive interface. The rotary drive interface may be a knob, an Allen wrench socket, a standard Phillips or flat blade screw driver socket, or another suitable drive interface. A rotationally fixed nut having a threaded aperture, such as a standard or special round or hex nut, engages the threaded rod and defines a first longitudinal axis of the assembly. A guide extends around the threaded rod. The guide is spaced away from the threaded nut and provides a second longitudinal axis different from the first longitudinal axis.
According to one aspect of the invention, one or more additional guides are provided along the length of the threaded rod to constrain it substantially within its relaxed or unloaded configuration. Alternatively, one or more of the additional guides are threaded nuts positionally fixed relative to the first threaded nut, thereby providing an additional threaded interface which increases the load transference ability of the threaded rod.
According to various aspects of the invention, the additional guides and extra threaded nuts define the trajectory of the threaded rod by constraining its progress to a predetermined path determined by the relative orientation between successive guides and threaded nuts situated along a path. The possible trajectories of the path are not limited by changes in direction or length. The threaded rod is configured to follow a 3-dimensional snake-like trajectory, with the additional guides and extra threaded nuts providing extra column strength by reducing the unsupported column length between guides and threaded nuts.
According to one aspect of the invention, the coil spring forming the threaded rod is a torsional spring having each coil compressively contacting an adjacent coil and wound in a direction such that rotation of the threaded rod that advances the threaded rod relative to the threaded hole tends to increasingly compress adjacent coils relative to one another. The increasing compression between adjacent coils stabilizes the thread pitch and reduces the friction, resulting in smoother motion of the threaded rod through the successive guides and threaded holes. For example, clockwise rotation is used with a right-hand thread to transmit the load, while counterclockwise rotation is used with the right-hand thread to return the coil spring to its initial position.
According to other aspects of the invention, a method is provided for advancing a longitudinally rigid threaded rod along a 3-dimensional curving course. The threaded rod is formed of a helical coil tension spring with an initial compressive force between adjacent coils. This initial compressive force between adjacent coils provides the force necessary to avoid unwinding of the spring coils otherwise resulting from frictional forces during counterclockwise rotation. The relatively incompressible adjacent coils provide relative rigidity along the spring""s longitudinal axis as defined by the individual longitudinal axes defined by adjacent coils. In other words, while the threaded rod is relatively incompressible along its length, the individual segments of the longitudinal axes defined by adjacent segments of the coils can be offset relative to one another to permit the threaded rod to follow a curving course. The spring is stiff in the direction of its axis, but flexible in other dimensions. The method of the invention therefore provides spatially fixing a threaded nut that defines a first longitudinal axis; orienting a rod guide that defines a second longitudinal axis that is different from the first longitudinal axis; and threading the coiled wire through each of the threaded hole and the guide. Optionally, additional guides and/or threaded holes are provided along the length of the intended curving course. A handle or other rotary interface is provided for rotating the threaded rod, which drives it through the threaded holes and along the rod guides. Thus, the threaded rod of the invention is optionally directed along a 3-dimensional trajectory without noticeable power losses.